Devices for varying or changing the angular phase relation or timing between an engine crankshaft and camshaft are well known. It is also known that such devices may utilize cyclic torque characteristics in an engine valve gear train to provide forces for effecting the phase changes. Examples of such devices utilizing the cyclic torque may be seen by reference to U.S. Pat. Nos. 3,721,220 to Garcea; 4,627,825 to Bruss et al; 5,002,023 and 5,046,460 to Butterfield et al; 5,056,477 to Linder et al; 5,056,478 to Ma; 5,056,479 to Larga; 5,078,647 to Hampton; and to published European Patent application 0,438,720. All of these references are incorporated herein by reference.
As disclosed in Pat. No. 5,078,647 to Hampton and herein, torque in the valve gear train includes a substantially constant, positive, noncyclic torque portion due to valve gear friction and in some engines due to valve opening overlap, positive torque pulses during valve opening and compression of the valve springs, and negative torque pulses during valve closing and driving of the camshaft by stored forces in the compressed valve springs. The substantially constant positive torque and the positive torque pulses are, of course, additive and occur when crankshaft torque is driving the phase change device and the camshaft. These positive torques are utilized by the devices of the above references to retard camshaft rotation relative to the crankshaft. The negative torque pulses subtract from the positive directed torque and may be utilized to advance camshaft rotation relative to the crankshaft.
In engine valve gear trains with relatively low constant positive torque, portions of the amplitudes of the negative torque pulses extend negatively below a zero torque reference of the positive directed torque and tend to drive the camshaft and phase change device in the same direction as the positive directed torque. In engines having valve gear trains with relatively high constant torque, portions of the amplitude of the negative torque pulses may not extend below the zero torque reference and therefore, are not available to effect camshaft phase advance. The negative pulses may be made available by transmitting all or part of the high constant torque to the camshaft with a bypass or splitter spring disposed in parallel with portions of the phase change device that utilize the negative torque pulses to advance the camshaft. Such splitter springs are disclosed in previously mentioned U.S. Pat. Nos. 5,046,460; 5,056,477 and 5,078,647.
The rotational phase change devices in previously mentioned U.S. Pat. No. 5,078,647 and application Ser. No. 0,438,720 employ one-way roller clutches to effect phase advance and retard in response to the negative torque pulses and the positive directed torque, respectively. In these references, the rollers may be selectively positioned to prevent retarding rotation of the camshaft in response to positive directed torque and to allow advancing rotation of the camshaft in response to the negative torque pulses. Conversely, the rollers may be selectively positioned to prevent the advancing rotation by the negative torque pulses and to allow the retarding rotation by the positive directed torque. The roller clutches in these devices allow the camshaft to be either fully retarded or advanced within a range determined by stops in the devices.
All of the above mentioned phase change devices have certain disadvantages which have prevented or limited their use in mass production. For example, they tend to be difficult to package in the limited space normally available, they tend to have prohibitive mechanical complexity and therefore are expensive, they tend to be unreliable, they tend to be difficult to control, and/or they operate slower than desired when changing phase angles. Certain of the above devices that are capable of phase modulation, i.e., intermediate phase angle positions between full retard and advance, are believed to operate too slow to fully utilize the modulation feature since intermediate phase angle positions are often needed during rapidly changing engine operating conditions. Further, the above roller clutch phase change devices are either incapable of phase modulation or do not reliably provide phase modulation.